Design optimization and comparative study of novel magnetic-geared permanent magnet machines

This paper presents a novel magnetic-geared permanent magnet (MGPM) machine with dual flux modulating effect. The key is to employ the PMs both on the outer rotor and in the modulation ring, which is referred as dual-layer MGPM (DL-MGPM) machine. Compared with the conventional flux modulating design, dual field modulating effect can couple the magnetic fields excited by the armature windings, the rotor PMs and the modulation PMs effectively. Comparative study is conducted between the proposed machine and its existing counterpart with all the PMs on the outer rotor, referred as single-layer MGPM (SL-MGPM) machine. Furthermore, both MGPM machines can work in two operation modes, that is outer rotor mode with the modulation ring kept stationary, and middle rotor mode with the modulation ring acting as the rotor, while the outer layer kept standstill. The electromagnetic performances of MGPM machines in the two operating modes are analyzed and quantitatively compared using finite element method (FEM). Both of machines are optimized, and comparison results show that the proposed DL-MGPM machine enjoys higher potential to be designed with larger torque density.